1. Field of the Invention
The invention relates generally to medical devices, and more particularly, to medical devices for repair of tissue, including intervertebral discs.
2. Description of Related Art
The spinal cord is the body's main nerve pathway, extending from the base of the skull down the back toward the lower (sacral) region of the back, where it branches. The spinal cord is protected from injury and damage by the vertebral column, a flexible column comprised of bones called vertebrae, which encircle and enclose the spinal column. Most of the vertebrae in the spinal column are interspersed with intervertebral discs, which are compliant discs, each approximately 1.0 cm to 1.5 cm thick. The discs are disposed between adjacent vertebrae in the spinal column and allow limited motion and rotation between those adjacent vertebrae. The cumulative effect of the motion provided by the disc allows the spinal column to flex and move. The discs also act as shock absorbers. The intervertebral discs themselves are comprised of a relatively tough outer layer called the nucleus purposus 222, inside of which is a soft, gel-like center called the nucleus purposus 224.
FIG. 1 is a plan view of a single vertebra, shown generally at 200, and its associated intervertebral disc 202. (The anatomy shown in FIG. 1 is generally that of a lumbar vertebra, although the anatomy of thoracic and lumbar vertebra is similar; therefore, FIG. 1 can be considered to illustrate the basic principles of both thoracic and lumbar vertebral anatomy.) The spinous process 206 of the vertebra 200 extends dorsally and can typically be palpated and felt through the skin of the back. Also in the dorsally-extending portion of the vertebra 200 are two transverse processes 208 and two mammillary processes and facet joints 212. A spinal canal 214 (i.e., an opening) is provided in the vertebra 200. The spinal cord and nerves 216 extend through the spinal canal 214 such that the spinal cord 216 receives the full protection of the bony, dorsally-located spinous, transverse, and mammillary processes and facet joints 206, 208, 212. The vertebral body also protects the spinal cord and nerves 216 ventrally. Periodically, nerves 218 branch out from the spinal cord 216 to innervate various areas of the body. The forward or ventral edge of the vertebral foramen 221 (see FIGS. 1 and 2) is defined by the vertebral body (not shown in FIG. 1), a bony, generally elliptical shelf in front of which the intervertebral disc 202 rests. FIG. 1 also illustrates the basic structure of the intervertebral disc 202, including the nucleus purposus 222 and the nucleus pulposus 224.
The vertebrae and the intervertebral discs are usually in good alignment, e.g., as shown in FIG. 1, and the intervertebral discs normally perform their function without incident. However, there are certain conditions, notably traumatic injury and vertebral column degeneration, that can cause problems. For example, if a weak spot develops in the nucleus purposus, the pressure on the disc may cause the nucleus purposus 224 to be pushed through the weak spot, a condition called herniation. This reduces the shock-absorbing ability of the disc, and may impinge on spinal or surrounding nerves, causing pain and possibly sensory or motor problems. Moreover, trauma may cause an intervertebral disc to fail entirely, potentially causing all of the above problems, even if a particular weak spot in the nucleus purposus has not developed.
FIG. 2 is a plan view similar to that of FIG. 1, illustrating a herniated or traumatized intervertebral disc 202. As shown, the nucleus pulposus 224 is protruding from the intervertebral disc 202 through a cut or flaw 204 in the intervertebral disc 202. The protruding nucleus pulposus 224 impinges on one of the exiting nerves 218 as well as the spinal cord 216 or cauda equina.
If an intervertebral disc has failed or become herniated, a typical correction is a surgical procedure to remove some or all of the herniated portion (or the protruding nucleus purposus 224) but no attempt is made to repair the nucleus purposus by surgically closing any hole or incision. FIG. 3 is a plan view similar to that of FIG. 1 showing partial results of a typical repair procedure in which the protruding nucleus pulposus 224 is removed and, depending on the procedure, the cut, incision, tear, or flaw 204 may be altered or neatened so as to provide for easier closure. In the view of FIG. 3, the cut, incision, tear, or flaw 204 is still open.
Any surgery to the vertebral column can be traumatic for the patient, and, depending on the area of the intervertebral column that is to be repaired, it can be difficult to access the area to make repairs. It is very difficult to close the nucleus purposus effectively; therefore no attempt is currently made to close or repair this defect.